Among the surface sheets for the absorbent articles are those using a composite sheet that is made by laying a sheet material on which a large number of protruding portions are formed on top of a smooth sheet material and joining the two sheet materials at positions in between the protruding portions. The composite sheet is to be worn in such a manner that the large number of protruding portions protrude toward the skin of a wearer, thereby providing a feeling of comfort to wear as well as preventing liquid leakage effectively.
Conventionally, as a shaping apparatus forming a large number of three-dimensional shapes such as the protruding portions on a sheet material, there has been one in which a pair of rolls (hereinafter referred to as shaping rolls as well) on circumferential surfaces of which recessed and protruding shapes are formed are disposed in such a manner that their recessed and protruding shapes mesh with each other (for example, refer to Patent Literature 1). In the shaping apparatus, a large number of three-dimensional shapes are formed on a sheet material passing between the pair of shaping rolls. Then the sheet material on which the three-dimensional shapes have been formed is conveyed along with the circumferential surface of the downstream shaping roll of the pair, laid on a smooth sheet as mentioned above, and then pressed by a pressing roll that is disposed on the downstream side; the predetermined portions of the sheets are joined together, and thus a composite sheet is produced.
The pair of shaping rolls need to rotate synchronously with each other so that the recessed and protruding shapes mesh with each other. To that end, it may be considered that a rotational driving means that is cooperatively coupled with the shaping rolls includes a transmission device consisting of, for example, timing pulleys and a timing belt that runs over the timing pulleys or the like in order that its output shafts to the respective shaping rolls rotate synchronously.
However, each of the pair of shaping rolls needs to be shifted in a direction perpendicular to its shaft center for adjusting the gap between the rolls, the depth of meshing, the pressing force and so forth depending on the recessed and protruding shapes, thicknesses of the sheet materials and so on. Then, in a case where output sections of the transmission device are directly coupled to the rotating shafts of the shaping rolls, the output shafts of the rotational driving means should also be shifted together with the shaping rolls being shifted, which is not easy.
Besides, even a slightly oblique deflection of the roll shaft centers of the pair of shaping rolls from their parallel disposition results in differences in the gap between the rolls, the depth of meshing, the pressing force and so forth between one end and the other end of the shaping rolls, thereby causing a problem that three-dimensional shapes formed on the sheet material become nonuniform. Therefore, the gap between the rolls, etc. must be adjusted minutely, which has been very troublesome.
In a case where the sheet material is a surface sheet, for example, the circumferential surfaces of the shaping rolls have fine recessed and protruding shapes densely formed thereon. Specifically, recessed shapes and protruding shapes of several millimeters each in diameter are formed around 1 mm apart, for example. Besides, the shaping rolls rotate at a rate of 600 to 800 rpm, for example; thus, the surface velocity of a roll main body reaches as much as 300 to 400 m/min, although it varies with the kind, thickness, etc. of the sheet material to be produced.
As a result, there is a risk that the sheet material, after passed between the pair of shaping rolls and conveyed on the circumferential surface of the downstream shaping roll to the next process is lifted off the roll surface having the recessed and protruding shapes due to a centrifugal force and thereby cannot maintain the predetermined three-dimensional shapes; and there is also a risk that, if there is a deviation of the three-dimensional shapes on the sheet material from the recessed and protruding shapes on the surface of the shaping roll, the three-dimensional shapes on the sheet material become deformed when pressed by the pressing roll disposed on the downstream side.
Further, in a case where the three-dimensional shapes that are formed on the sheet material tightly fit the recessed and protruding shapes that are formed on the downstream shaping roll, it is not easy to separate the sheet material from the surface of the downstream shaping roll at the position where the sheet material is sent out to the next process; this may place an obstacle to sending it out to the next process and thus increases the risk that the sheet material winds around the downstream shaping roll. Thus, there has been a problem that, with use of the conventional shaping apparatus, sufficiently high shaping speed of three-dimensional shapes is not easily attained.